1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotographic technique.
2. Related Background Art
Conventionally, there has been an image forming apparatus in which there has been adopted transferring material conveying means (transferring material conveying belt) for bearing and conveying a belt member for transferring a toner image on an image bearing member onto transferring material in the image forming apparatus, that is, an intermediate transferring member (intermediate transferring belt) for bearing a toner image to be transferred from the image bearing member, or transferring material for transferring the toner image from the image bearing member.
In the image forming apparatus equipped with the belt member, when the belt member is driven, the belt member tends to shift along a direction of an axis of a member to rotate the belt member as a particularity of a belt mechanism. For example, the belt member tends to shift along a lateral direction. Therefore, it is required that these kinds of shifts of the belt member be restrained. In claims and descriptions in this specification, the term “a lateral direction (shift direction)” is hereinafter used as meaning a direction along which a belt member shifts. As a mechanism for correcting the shift of the belt member, there have been conventionally several types of mechanism as shown in i) to iv).
i) A mechanism for regulating the inclination of the belt member in which the belt member has a rib, and the rib portion is caused to enter a groove provided on a supporting member which supports the belt member to thereby regulate a moving range of the rib within the groove.
ii) A mechanism for correcting the inclination of the belt member by detecting an inclination state of the belt member, transmitting the detection result electrically, and in response to the result, forcefully causing the supporting member which supports the belt member to change its angle through the use of an actuator consisting of a stepping motor and the like.
iii) A mechanism for adjusting an angle of the supporting member which supports the belt member by receiving, when the belt member shifts along a lateral direction (shift direction), a force in the lateral direction.
iv) A mechanism in which a force of movement of the belt member in the direction of rotation is inputted by drive receiving means provided at the end portion of the supporting member, coming in contact with the back surface of the belt member, and the angle of the supporting member is changed by the force of movement of the belt member.
However, the above-described structure of i) to iv) has the following problems.
In the mechanism of i), since the rib is to receive a reaction of the force of inclination of the belt member, a strong force is exerted on the rib when the inclination occurs, and the force is exerted on the belt member to further deterioration of the durability of the belt member.
The mechanism of ii) results in complicated mechanism such as supply of electricity being required around the belt member.
In the mechanism of iii), since an inclination speed of the belt member is generally slow, response of the supporting member to the change in angle is slow.
In the mechanism of iv), the flatness of the belt member may not be secured, or strain may occur.